1) Field of the Invention
This invention relates to seal assemblies and, in particular, to a pressure-actuated seal assembly for controlling the flow of a fluid along a shaft.
2) Description of Related Art
Various applications require the formation of a seal along a shaft or other rotatable member. For example, turbopumps that are used in rocket engines typically include a turbine and a pump that are connected by a shaft. The turbine is rotated by the flow of a fluid, thereby rotating the pump, which pumps another fluid. In some cases, it is desirable or necessary to separately maintain the fluids in the turbine and the pump. For example, leakage of a liquid from the pump can energetically react with fluid that is being used to rotate the turbine.
One or more seals are provided between the turbine and pump to control the flow of fluids therebetween or to overboard drains located between the pump and turbine. However, due to the high rotational speed of the components of the turbopump, contact between the stationary seals and the rotating shaft can result in excessive wear of the seals as well as the generation of heat that can negatively affect the performance or safety of the turbopump. Thus, lift-off seals can be provided between the turbine and the pump, each lift-off seal being configured to adjust between open and closed positions. In the closed position, the lift-off seal is biased by a spring against a surface of the shaft. The spring can be overcome by a pressurized fluid, e.g., from the pump or from an external source, to move the lift-off seal away from the surface of the shaft to the open position. Thus, at low speeds of operation, when the pressure in the pump is low, the spring maintains the lift-off seal in the closed position to limit the flow of fluid from the pump. During higher speeds of operation, when the pressure in the pump is higher, the lift-off seal is adjusted to the open position. Typically, migration of the fluid from the pump is at least partially prevented during higher speeds of operation by a non-contacting sealing mechanism. For example, a slinger connected to the shaft can define blades that extend radially outward therefrom to rotate the fluid at the pump side of the seal. The rotation of the fluid forces the fluid radially outward beyond the lift-off seal to prevent the fluid from leaking through the space opened between the lift-off seal and the shaft.
While conventional seals do provide some degree of sealing between such components as the turbine and pump of a turbopump, there exists a need for an improved seal and method for controlling the flow of fluids along a shaft. In particular, the seal should maintain a high degree of sealing, while also limiting the heat and wear that results from contact between sealing members at high speed operation.